1. Field of the Invention
The present invention relates to a display device, and more particularly to a display device with an integrated touch screen.
2. Discussion of the Related Art
A touch screen is an input device included in image display devices such as Liquid Crystal Displays (LCDs), Field Emission Displays (FEDs), Plasma Display Panel (PDPs), Electroluminescent Displays (ELDs), and Electrophoretic Display (EPDs), and allows a user to input information by applying a pressure (i.e., pressing or touching) to a touch sensor of a touch screen. The demand of display devices with integrated touch screens such as smart phones and tablet Personal Computers (PCs) is increasing.
Hereinafter, a related art display device with an integrated in-cell type touch screen will be described with reference to FIG. 1. In particular, FIG. 1 is a diagram illustrating a related art display device with an integrated self-capacitive touch screen having an in-cell type.
As shown, the related art display device includes a panel 10 with a plurality of built-in electrodes 12, a display driver IC (DD-IC) 20 connected to an external system and controlling a plurality of data lines 13 inside the panel 10, and a touch IC 30 that drives the electrodes 12 inside the panel 10. Further, the panel 10 is alternately driven in a display driving mode and a touch driving mode, and thereby performs a touch function and a display function.
When the driving mode of the panel 10 is the display driving mode, the electrodes 12 receive a common voltage through a connection line 23 to act as a plurality of common electrodes for display driving, and the data lines 13 receive a floating voltage or a ground voltage from the display driver IC 20 for driving the liquid crystal display device.
Moreover, when the driving mode of the panel 10 is the touch driving mode, the electrodes 12 receive a touch scan signal through the connection line 23 to act as a plurality of touch electrodes. As shown in FIG. 1, the connection line 23 is connected to the electrodes 12.
Thus, in the related art display device, an initial capacitance is generated between a touch electrode and a data line, and the higher the initial capacitance, the lower the touch sensation. The reason is as follows.
A touch sensation corresponds to a size of a signal to noise ratio (SNR), which is a value obtained by dividing an average value of a signal (which is generated when a touch is not performed) and a signal (which is generated when a touch is performed) by the maximum value of noise caused when a touch is not performed. Therefore, the greater the noise, the less the size of an SNR, and thus the higher the initial capacitance and the lower the touch sensation. Further, the noise value is the initial capacitance value.
Hereinafter, an initial capacitance that lowers a touch sensation as described above will be described in detail with reference to FIG. 2. In particular, FIG. 2 is an enlarged diagram of a portion A of FIG. 1 illustrating the related art display device.
As illustrated in FIG. 2, an initial capacitance of 2.85 pF is formed between electrodes 12, and an initial capacitance of 1.6 pF is formed between data lines 13. Also, an initial capacitance of 98.5 pF is formed between an electrode 12 and a data line 13 that is formed not to overlap the electrodes 12, and an initial capacitance of 25.3 pF is formed between an electrode 12 and a data line 13 that is formed to overlap the lower portion of the electrode 12.
As shown in FIG. 2, an initial capacitance formed between an electrode 12 and a data line 13 is relatively greater than an initial capacitance formed between electrodes 12 or an initial capacitance formed between data lines 13. Therefore, an initial capacitance formed between an electrode 12 and a data line 13 causes relatively greater noise compared to an initial capacitance formed between electrodes 12 or an initial capacitance formed between data lines 13. Thus, a touch sensation is lowered.
Therefore, even though the floating voltage or the ground voltage is applied to a data line in the touch driving mode, a touch malfunction can occur when the floating voltage is applied to a data line in the touch driving mode, and an initial capacitance increases when the ground voltage is applied to a data line in the touch driving mode, causing an increase in noise. Further, a touch sensation and the accuracy of a touch are lowered due to an initial capacitance formed between an electrode and a data line.